1. Field of the Invention
The invention relates to a process for transesterifying esters of unsaturated carboxylic acids with reactive alcohols and with a catalyst for these processes.
2. Description of the Background
It is known to prepare carboxylic esters by transesterification.R—COOR′+R″—OH→R—COOR″+R′—OHR generally represents an aliphatic or aromatic group, R′ may be for example methyl or ethyl, and R″ is a group which may contain more carbon atoms than R′. R′ and R″ may be selected so that the alcohol formed is more volatile than the ester. The use of a catalyst speeds equilibration.
The present invention relates to the synthesis of t-butylaminoethyl methacrylate by transesterification of t-butylaminoethanol with methyl methacrylate (MMA). The transesterification is known per se. JP 062717517 and JP 06256271 describe the transesterification of methyl methacrylate with t-butylaminoethanol under K2CO3 catalysis. Disadvantages here are the relatively long reaction time (5 hours) and the appearance of byproducts (91% purity), so that the product has to be purified by distillation.
JP 62185059 and JP 62175448 describe the synthesis of diethylaminoethyl methacrylates in the presence of K2CO3, Rb2CO3, Cs2CO3. The purity achieved is above 95%, but the reaction still takes 5 hours.
JP 62242652 describes the use of KHCO3 as a catalyst. Disadvantages here are that the reaction likewise takes 5 hours and a distillation is needed to purify the crude product. Generally, alkaline catalysts lead increasingly to double bond adducts, especially in the presence of amines.
EP 298867 describes catalysis by means of titanium (IV) alkoxide. It is to be noted that this method too requires a distillative workup to obtain a purity >98%. Titanium catalysts are also H2O sensitive, which makes the synthesis more costly and more inconvenient to perform.
JP 62230755 describes K3PO4 catalysis. The disadvantage is again the reaction time of 5 hours for a conversion of 83.5%.
JP 56104851 utilizes dibutyltin oxide as a catalyst. This catalyst has the disadvantage that 8 hours are needed for a conversion above 95%.
Alkali metal oxides are disclosed in FR 1568382 and GB 1174148. The disadvantage here is that conversions are <95% and the yield is only slightly above 80%.
EP 160427 (Allied Colloids) describes the transesterification of methacrylates in the presence of an alcohol and/or in the presence of a mixture of alkoxides of that alcohol and/or of methanol with Ca, Mg or Ba, Ti and Zr or Al. The catalyst is recyclable.
The prescription is to transesterify dimethylaminoethanol (DMEA) with MMA to form DMAEA (dimethylaminoethyl methacrylate). The disadvantage here is that the alcohol first has to be converted into the metal alkoxide (which is costly and inconvenient to do) in order then to be used in a large amount in the synthesis (DMEA ligand:MMA=3:4).
EP 118 639 (Allied Colloids) describes a transesterification process catalyzed by metal alkoxides of metals Ti, Al, Zr, Ca or Mg.
U.S. Pat. No. 2,138,763 describes the transesterification of methyl methacrylate with different amino alcohols in the presence of sodium methoxide.
A reaction has to be carried out in the absence of water and reactive alcohols. The best results are achieved with calcium or magnesium as metal component. Nothing is said about the by-product spectrum.